Texture amount limit per one material?
Dirty workaround is to enable Open Shading Language in render tab (works only with CPU), somehow it solved my problem, even though I don't have a clue what does it mean.
Another trick is to use spritesheet technique. In a nutshell, you have to combine all your images into 1 big image (without overlaying of course) and translate UV map along these "small" images. In this setup you are duplicating Vector Mapping as many times as there are images on the spritesheet.